Description: The Flow Cytometry Facility, originally established in 1980, has evolved since the last review with the application of flow cytometry to new types of analyses. The facility currently provides the following services: 1) multi-parameter flow cytometry allowing analysis of up to five different antigens using immunofluorescence phenotyping; 2) measurements of apoptosis and cell cycle status using fluorescent DNA labeling; 3) measurement of cellcell interactions (intercellular conjugation); 4) separation and purification of cell lines by FACS; 5) technical support in terms of protocol design and data analysis as required by the investigators; 6) investigator training to perform data acquisition and analysis; and 7) electronic storage, archiving and retrieval of flow cytometric data. The Flow Cytometry resources are available on a first come, first served basis, unless usage for a specific project far exceeds the norm expected to maintain equal access. In that case, Dr. Spain and Mr. Faust will prioritize the various proposals. The machines, however, are available 24 hour a day after regular hours without operator assistance. Four cytometers are available. The Coulter EPICS XL-MCL is a state-of-the-art benchtop cytometer with fixed alignment and an automated sample change carousel. This machine is capable of processing 32 samples automatically at 100 samples/hr. The Ortho Cytofluorograf 50HH has been reconfigured to handle 120 to 180 samples/hr, including the generation of complete numerical data and hard copies. The Coulter EPICS Elite is the most advanced instrument at Wistar and is capable of five-color analysis and sorting. The Becton-Dickinson FACScan Flow Cytometer System is a single argon laser instrument equipped to measure three scatter and 3 fluorescent parameters. It also contains a module for DNA analysis. In 1995, over 1,000 hours of instrument usage by 19 investigators with 27 grants are documented. There is no charge for the use of the FACScan or Coulter EPICSXL-MCL by investigators who use the equipment without assistance. Charges are levied for use with an operator at $50/hour for analysis and $50/hour for the first hour and $30/hour for each additional hour for sorting. In 1995, the total amount collected for 1000 hour of usage was $16,021. The use and operation of this facility is overseen by the Wistar Biotechnology Committee chaired by Dr. William Wunner. The other members are Dr. Giorgio Trinchieri, the Facility Director, Mr. Jeffrey Faust, manager and Dr. Spain, who supervises the FACScan.